Roller chain comprises an assembly of laterally spaced pairs of roller link plates joined by bushings which are press fitted into apertures in the roller link plates, and laced together with pairs of laterally spaced pin link plates flanking the roller link plates. Pins passing through the bushings and through apertures in the pin link plates join adjacent roller link plates assemblies. Various methods may be employed to integrate the assembly, as for example, upsetting the ends of the pins, using headed pins or retaining washers and/or cotter pins, depending upon a press fit, etc. A roller surrounds and is rotatable about each bushing; a roller being assembled onto a bushing during the press fitting operation. The chain may be assembled in continuous lengths, after which sections are broken out and the ends of a section are joined, usually by a connecting link, to make an endless chain for use in a chain-sprocket drive. At other times, the chain is assembled in an endless configuration. Automatic or semi-automatic machinery may be used to manufacture roller chain, or the chain can be assembled by hand.
Bushings are formed by curling and die forming finite lengths of steel strip into circular cylinders by processes known in the art. The particular process described for forming the bushings is, in the applicant's opinion, the best and most economical, but other processes can be used if desired. It is important to note that each bushing so formed includes a seam where the ends of a finite length of strip meet. In some chain assembly processes, the formed bushings are assembled randomly with the roller link plates while in other chain assembly processes the formed bushings are oriented so that the seams are located on the side of the bushing which does not carry a load from the pin. When the assembly process includes orientation of the bushings, each finite length of stock, when cut, is provided with an indentation or cut-out, generally centrally located at the cut, so that when the bushing is formed, an opening or slot is provided. The smaller pitch chains usually include the slot while larger pitch chain may include a generally circular, diamond shaped, or rectangular opening. The slot or opening is bisected by the seam at the juncture of the ends of the strip. Orientation of the bushings is accomplished by using equipment which engages the slot or opening and which then positions the bushings for press fitting into the roller side plates.
Roller chain horsepower capacity is limited by several factors, i.e., link plate fatigue, roller-bushing impact, and pin-bushing galling. In larger sizes of roller chain (11/2 inches pitch and larger) used for industrial applications, the pin-bushing galling factor affects the major part of the horsepower capacity curves or tables. Studies relating to speed limits at which galling begins have been made. However, practical experience permits drives using roller chain to operate at higher speeds than those indicated by the studies with some galling. Operation at these higher speed limits can be accomplished with careful attention to lubrication and cooling, but of course, with some risk of failure.
Because the galling limit affects a considerable part of the horsepower curve, anything done to increase the maximum operating speeds will increase the potential applications of roller chain in the market place, and will have economic benefits to the manufacturer and also to the users of roller chain.
The pin and bushing of roller chain constitute a journal bearing assembly, and thus journal bearing analytical procedures are applicable with some special limitations. The pin-bushing is not a rotating bearing in the same sense as a journal bearing but rather oscillates as the chain articulates when entering and leaving the sprockets with which it is coupled as a drive. Maximum articulation of the joint (the pin-bushing) is approximately 20 degrees or less as the number of teeth in the sprocket increase. When the pin-bushing (joint) is in the tight or driving strand, the nominal bearing pressure, i.e., strand pressure divided by projected area of pin-bushing, may reach levels in excess of 5000 psi. In the tight strand at these pressures, essentially metal-to-metal contact is present. Bushing barrelling, the deformation of a bushing into a barrel-shaped member having reduced diameter ends, which results from the press fitting of the bushing into the roller link plates and surface asperities present on the pin and bushing result in still higher unit pressures.
Studies have shown that during articulation, a hydrodynamic film or at least a partial hydrodynamic film is generated at the pin-bushing interface. If the supply of oil or other lubricant to the pin-bushing contact area can be enhanced and/or increased, the initiation of the film will start earlier in the articulation and provide enhancement of the lubrication of the joint.
The invention herein described provides for enhanced lubrication of the pin-bushing interface and thus permits the higher speed use of roller chain without encountering serious galling problems and without a material increase in the cost of manufacturing the chain.